7 binders cost $12.18. Which equation would help determine the cost of 9 binders?
There are several equations that could help determine the cost, each with a slightly different approach. We can write the fact that 7 binders cost $12.18 as a proportion: $\dfrac{7}{\$12.18}$ Let $x$ represent the unknown cost of 9 binders. Since 9 binders cost $x$ , we have the following proportion: $\dfrac{9}{x}$ The cost changes along with the number of binders purchased, and so the two proportions are equivalent. $\dfrac{7}{\$12.18} = \dfrac{9}{x}$